And note also that even if you hypothesize "different genes to perform a similar function" of speech in Neanderthals and Cro-Magnons, there are no known modern humans that evidence this alleged Neanderthal alternative to the unique human FOXP2 gene. So, that would be yet another sign that Neanderthals and Cro-Magnons did not intermix, because if they did then you would plausibly expect to find some descendents with this hypothetical Neanderthal speech-enabling alternative.
http://64.233.179.104/search?q=cache:J_SUa7DC0akJ:www-personal.umich.edu/~wolpoff/Papers/Why%2520not%2520the%2520Neanderthals.pdf+FOXP2+GENE+BLACKS&hl=en&gl=us&ct=clnk&cd=8
I haven't had time to read the entire article, just skimmed over it because I need to get to work. But it appears quite interesting - would like your comments.
Have a good day.